Hands-free kit for mobile radio-telephone handset

ABSTRACT

A hands-free kit for a mobile radio-telephone handset, the hands-free kit having an earpiece and an infra-red transmitter with the transmitter being able to relay audio signals from the handset to the earpiece. The earpiece includes an infra-red receiver for receiving audio signals from the transmitter. By positioning the transmitter in the line of sight of the earpiece receiver, audio signals may be relayed from the handset to the earpiece with the reduced likelihood of the earpiece becoming dislodged as the user moves his head.

[0001] The present invention relates to a hands-free kit for a mobile radio-telephone handset.

[0002] Concerns have recently grown over the safety of mobile radio-telephones handsets, otherwise known as cellular phones, which have been found to emit high levels of microwave radiation.

[0003] To reduce the risks associated with such handsets, a number of hands-free kits have been devised which connect an earpiece and microphone to a handset via wires, thereby allowing the handset to be located a safe distance from the user's head.

[0004] However, it has been found that the earpieces of such kits are easily dislodged by tension on the connecting wires caused, for example, by the wires catching on the user's outer garments as he moves his head.

[0005] More importantly, it has recently been suggested that the connecting wires of such kits act as a conduit, channelling microwave radiation from the handset to the user's head.

[0006] We have now devised an arrangement which overcomes the limitations of existing hand-free kits for mobile radio-telephone handsets.

[0007] According to a first aspect of the present invention, there is provided a hands-tree kit for a mobile radio-telephone handset, the kit comprising an earpiece and an infra-red transmitter, the transmitter being arranged to relay audio signals from the handset to the earpiece, the earpiece comprising an infra-red receiver for receiving audio signals from the transmitter.

[0008] Thus, by positioning the transmitter in line of sight of the receiver, audio signals may be relayed from the handset to the earpiece with the reduced likelihood of the earpiece becoming dislodged as the user moves his head.

[0009] The transmitter may communicate with the handset via a wired or wireless connection, such as a radio frequency connection provided by Bluetooth® or Bluetooth®-type communications devices.

[0010] The receiver may be located at the distal end of a portion of the earpiece which, in use, projects forwards from the user's ear.

[0011] Preferably the receiver comprises a plurality of photosensitive devices arranged to receive infra-red signals from different respective directions including the direction of the transmitter.

[0012] Alternatively, the earpiece may comprise means, provided on a forwards projecting portion of the earpiece, for reflecting audio signals from at least the direction of the transmitter towards the receiver.

[0013] The transmitter is preferably arranged to be carried in the user's breast pocket or worn on the user's front, in line-of-sight of the earpiece receiver or of the reflecting means, and may be provided with means for attaching to an outer-garment worn by the user. For example, the attaching means may comprise a clip or pin for attaching the transmitter to the breast pocket or the lapel of a jacket or to a necktie.

[0014] Alternatively the transmitter may be permanently mounted to, or provided with means for temporarily attaching to, a part of a vehicle, for example the vehicle dashboard or a seatbelt, in line-of-sight of the earpiece receiver.

[0015] Preferably, the hands-free kit also comprises a microphone for connecting to the handset, the microphone preferably comprising part of an integrated unit also comprising the transmitter.

[0016] Where the transmitter communicates with the handset via a wireless connection, the microphone preferably also communicates with the handset via the same wireless connection.

[0017] The transmitter may be powered from the power supply of the handset or may comprise its own re-chargeable porter supply.

[0018] The earpiece preferably comprises a re-chargeable power supply, which may be arranged to be re-charged via a mains adapter or by plugging the earpiece, either directly or via an adaptor, into the cigarette lighter socket of a vehicle.

[0019] Most preferably the kit comprises a holder for the earpiece and the transmitter via which respective re-chargeable power supplies of the two devices may be charged.

[0020] The holder may be arranged to charge the earpiece and transmitter either directly from an external supply or via its own re-chargeable supply, to enable the earpiece and transmitter to be charged in the absence of said external supply.

[0021] Typically, from a full state of charge, the power supply of the transmitter will be exhausted sooner than that of the earpiece. To ensure that the transmitter is charged for at least as long as the earpiece, the holder is preferably arranged prevent the earpiece from being charged independently of the transmitter. For example, an electrically conductive part of the transmitter may be arranged to bridge a pair of contacts of the holder to complete a charging circuit for the earpiece. Thus, both the transmitter and the earpiece must be fitted to the holder before the latter can be charged.

[0022] The holder may also or otherwise be arranged to prevent the transmitter from being charged independently of the earpiece.

[0023] The holder may be provided with means for visibly indicating its state of charge and/or the state of charge of the transmitter and/or of the earpiece. However, the transmitter and the earpiece preferably comprise independent means for visibly indicating their respective states of charge, the holder preferably comprising a lidded case having a portion which is at least partially transparent and through which the charge indicating means of the transmitter and earpiece may be viewed.

[0024] In either case, the indicating means preferably comprise respective lights, e.g. light emitting diodes, which may, for example, be constantly illuminated, extinguished or illuminated intermittently to indicate different states of charge.

[0025] Most preferably the transmitter and earpiece each comprise a respective light which is illuminated intermittently when the device is operating (to indicate that the device is charged), is constantly illuminated when the device is being charged and is extinguished when the device has exhausted its power supply.

[0026] Preferably the earpiece emits an audible warning signal to indicate when the power supply of the transmitter and/or the earpiece is nearing exhaustion. Preferably the earpiece emits a periodic audible signal, with the frequency of the emitted signal increasing as the power supply of the earpiece and/or the transmitter is exhausted. For example, the earpiece may emit an audible signal every 5 minutes when there is between 5 and 30 minutes of charge remaining in the transmitter and/or the receiver, every 1 minute when between 30 seconds and 5 minutes of charge remains and every second when less that 1 second of charge remains.

[0027] Signals transmitted from the transmitter to the receiver may be encrypted.

[0028] The transmitter and receiver may be arranged to respectively encode and decode signals using a unique encryption algorithm.

[0029] Alternatively, the transmitter and receiver may be arranged to respectively encode and decode signals using one of a plurality of encryption algorithms chosen on a random basis, the number of possible encryption algorithms being sufficient to ensure an acceptably low likelihood of the same encryption algorithm being used by two transmitter/receiver pairs in the same vicinity.

[0030] In either case, the transmitter and receiver may be pre-programmed with an appropriate encryption key. However, the encryption key is preferably transmitted from the transmitter to the receiver, having preferably been generated by the transmitter.

[0031] Where the encryption key is generated by the transmitter, the encryption algorithm may, for example, be derived from the phone number or other identification code of the handset with which the hands-free kit is to be used, or a new key, chosen at random, may be transmitted to the receiver on a periodic basis, for example each time the transmitter is charged.

[0032] The transmitter may also or otherwise be arranged to transmit an identification signal to identify itself to the earpiece.

[0033] The identification signal may be unique or may be chosen at random from one of a plurality of possible signals, the number of possible signals being sufficient to ensure an acceptably low likelihood of the same identification signal being used by two transmitter/receiver pairs in the same vicinity.

[0034] In either case, the transmitter and receiver may be pre-programmed to operate using a particular identification signal. However, the identification signal to be used is preferably communicated from the transmitter to the receiver, having preferably been generated internally by the transmitter.

[0035] Where the identification signal to be used is generated by the transmitter, the signal may, for example, be derived from the phone number or other identification code of the handset with which the hands-free kit is to be used, or a new signal, chosen at random, may be communicated to the earpiece on a periodic basis, for example each time the transmitter is charged.

[0036] The earpiece may be arranged to respond to an invalid identification signal by emitting an audible warning signal.

[0037] The transmitter is preferably arranged to periodically transmit said identification signal.

[0038] The earpiece may be arranged to provide an audible alarm signal it a valid identification signal is not received over a pre-determined period of time.

[0039] Most preferably, the earpiece is arranged to operate for periods in a standby mode, wherein one or more functions of the earpiece are disabled to conserve power, the earpiece preferably being arranged to enter the standby mode in the absence of a received signal or if a valid identification signal is not received. The or each disabled function is preferably restored in response to a received signal, preferably only if that signal comprises a valid identification signal.

[0040] Entry into the standby mode may be immediate or may be delayed in one or more of the above circumstances.

[0041] For example, the earpiece may be arranged to enter a standby mode in the absence of a received signal or if a valid identification signal (such as one transmitted periodically by the transmitter) is not received over a pre-determined period of time. Preferably, the earpiece will then return to full functionality only on receiving a valid identification signal.

[0042] The transmitter is preferably arranged to operate for periods in a standby mode, wherein one or more functions of the transmitter are disabled to conserve power, in the absence of an audio signal from the handset.

[0043] We have found that, in use, the amount of infra-red light received by the earpiece receiver from the transmitter varies as a user moves his head. We have also found that a high level of ambient light can corrupt the infra-red signals received by the earpiece.

[0044] To counteract these effects, the hands-free kit may be arranged to transmit infra-red light of a constantly high level of intensity, such that the receiver is certain to receive the infra-red light emitted by the transmitter over a range of orientations of the user's head and over a range of ambient light levels.

[0045] However, such an arrangement in clearly wasteful of the limited amount of power available to the transmitter as, except in a few extreme conditions, only a low intensity of infra-red light need be emitted by the transmitter.

[0046] To reduce the level of power consumption of the transmitter, whilst ensuring that an adequate signal is always received by the earpiece receiver, the hands-free kit therefore preferably comprises a second infra-red receiver, located adjacent the transmitter, and means for varying the intensity of the infra-red light emitted by the transmitter according the amount of infra-red light received by the second receiver.

[0047] The earpiece preferably comprises means for reflecting a portion of the infra-red light emitted by the transmitter back towards the second receiver.

[0048] The reflecting means preferably comprise a part-spherical, multi-faceted arrangement of mirrors, which is preferably located at the distal end of the forward projecting portion of the earpiece. Each facet preferably comprises a respective concave parabolic mirror.

[0049] An alternative means for optimising the amount of light received by the earpiece from the transmitter in accordance with the present invention, is to provide a set-up mode, wherein the transmitter emits a light signal of substantially constant amplitude and the earpiece emits a periodic audible signal, whose periodicity varies in accordance with the amount of light received from the transmitter as the position of the transmitter is adjusted by a user, for example by increasing in frequency with the amount of light received from the transmitter.

[0050] According to a second aspect of the present invention, there is provided a mobile radio-telephone arrangement comprising an earpiece and a mobile radio-telephone handset comprising an infra-red transmitter for relaying audio signals from the handset to the earpiece, the earpiece comprising an infra-red receiver for receiving audio signals from the transmitter.

[0051] According to a third aspect of the present invention, there is provided a mobile radio-telephone arrangement comprising a mobile radio-telephone handset and a hands-free kit comprising an infrared transmitter located at the breast of a user for relaying incoming audio signals from the handset to an earpiece worn by the user, the earpiece comprising an infra-red receiver for receiving audio signals from the transmitter

[0052] According to a fourth aspect of the present invention, there is provided an earpiece for attaching to an ear of a user and comprising an infra-red receiver.

[0053] Preferably the receiver is arranged to receive signals from an infra-red transmitter positioned at the breast of a person wearing the earpiece.

[0054] A preferred embodiment of earpiece comprises a tail portion for hooking around the ear of the wearer, a portion which extends over and forwards from the user's ear and a portion which extends rearwards from the front of the device to position a microphone over the external auditory canal of the wearer.

[0055] Preferably an elastomeric grip is fitted to the tail portion of the earpiece, which is preferably replaceable to allow the shape of the device to be readily modified to fit different sized and shaped ears and the device to be personalised to the wearer's taste by replacing the grip with one of a different colour.

[0056] Preferably the front of the earpiece is provided with a window, behind which a pair of photosensitive devices are arranged to receive infra-red signals from different respective directions.

[0057] Preferably the tail portion of the earpiece houses electronic circuitry and a rechargeable power supply.

[0058] Preferably the microphone is rotatable about the axis of the rearwardly projecting portion, to enable the earpiece to be configured for fitting to either the left or the right ear of the wearer.

[0059] Preferably abutting parts of the rearwardly projecting portion and a housing of the microphone ensure that the microphone can only be rotated through 180 degrees between its left and right handed orientations.

[0060] According to a fifth aspect of the present invention, there is provided an audio apparatus comprising a headset, an infra-red transmitter for transmitting audio signals to the headset, an infra-red receiver located adjacent the transmitter and means for varying the intensity of the infra-red light emitted by the transmitter according to the amount of infra-red light received by the receiver.

[0061] Preferably the headset comprises means for reflecting a portion of the infra-red light emitted by the transmitter towards the receiver.

[0062] Embodiments of the present invention will now be described by way of examples only and with reference to the accompanying drawings, in which:

[0063] FIGS. 1 to 3 are respectively a front view, a side view and a rear view of a person wearing an apparatus in accordance with the present invention;

[0064] FIGS. 4 to 6 are respectively a front view, and perspective views from each side of a first embodiment of earpiece in accordance with the present invention;

[0065]FIG. 7 is a front view showing the earpiece of FIGS. 4 to 6 opened for fitting to a person's ear;

[0066]FIG. 8 is a side perspective view showing the earpiece of FIGS. 4 to 6 fitted to a person's ear;

[0067]FIG. 9 is a side view of a second embodiment of earpiece in accordance with the present invention;

[0068] FIGS. 10 to 13 are respectively views from opposite sides and two perspective views of a third embodiment of earpiece in accordance with the present invention;

[0069] FIGS. 14 to 16 are respectively a front and rear views and a perspective view of an embodiment of transmitter unit in accordance with the present invention; and

[0070] FIGS. 17 to 21 are respectively three perspective views, a view of the underside and a front view of an embodiment of holder in accordance with the present invention.

[0071] Referring to FIGS. 1 to 3 of the drawings, a person 2 is shown wearing a hands-free kit in accordance with the present invention.

[0072] The hands-free kit comprises an earpiece 4 and a transmitter unit 6, clipped to the breast pocket 8 of the person's jacket, for relaying audio signals from a mobile radio telephone-handset (not shown), via an infra-red transmitter of the unit, to an infra-red receiver 10 of the earpiece 4.

[0073] The transmitter unit 6 also comprises a microphone, with audio signals being transmitted from the handset to the infra-red transmitter of the unit and from the microphone to the handset, via either a wired or a wireless link, so that the handset may be located a safe distance from the user's head.

[0074] The earpiece 4 is arranged to become activated upon receiving an audio signal from the transmitter unit 6, it preceded by a valid identification code, to provide an audible output of the audio signal via a speaker 14 adjacent the user's ear 12.

[0075] The transmitter unit 6 is arranged to periodically retransmit the identity code within an audio stream, the earpiece 4 being arranged entering a standby mode, to conserve power, in the absence of a received signal or where a valid identity code is not received within a period of time.

[0076] The transmitter unit 6 is also arranged to enter a standby mode, to conserve power, in the absence of a signal from the handset. The transmitter unit 6 and earpiece 4 are powered by respective rechargeable supplies and are re-charged by fitting the two parts to a holder, such as that described in detail below. As the power supply of the earpiece 4 and/or the transmitter unit 6 is nearing exhaustion, the earpiece 4 periodically emits an audible warning signal whose frequency increases, the nearer the power supply of either unit comes to being fully discharged.

[0077] Each time the transmitter unit 6 and earpiece 4 are fitted to the holder for charging, a new identification code is generated at: random by the transmitter unit 6 and communicated to the earpiece 4, by which the earpiece 4 can then identify audio signals originating from that transmitter 6.

[0078] The earpiece 4 is also arranged, for example by pre-programming the earpiece or by programming the earpiece in-situ, to generate an audible output of received audio signals preceded by at least one other identification code, such as may be assigned to an infra-red transmitter installed in a public facility or retail outlet, the earpiece 4 preferably being arranged to give precedence to signals identified as having been received from the transmitter unit 6.

[0079] To facilitate the reception of audio signals from sources other than the transmitter unit 6, the infra-red receiver 10 of the earpiece 4 comprises a pair of photosensitive devices, one of which is directed downwards towards the transmitter unit 6, the other being directed upwards to receive signals from said other sources.

[0080] The transmitter unit 6 is also provided with an infrared receiver (not shown), adjacent the infra-red transmitter thereof, for adjusting the level of intensity of infra-red signals emitted from the unit, according to ambient light levels.

[0081] A first embodiment of earpiece 4 is shown in detail in FIGS. 4 to 6. Two part-cylindrical halves 16, 18 of a clip 20 are hingedly joined together along the top of the earpiece and are each lined with a cushioning material 22. A telescopic rod 24 extends forwards from the clip 20 and is provided at its distal end with an infra-red receiver 26. A portion of the rod, also at its distal end, is touch-sensitive for activating and de-activating the electronic circuitry of the earpiece. In its retracted position, the projecting portion of the rod 24 is arranged to fit either directly, or via an adaptor, into the cigarette lighter socket of a vehicle to recharge the power supply of the earpiece via electrical contacts on the exterior of the rod.

[0082] The distal end of the rod 24 may also be provided with a part-spherical mirrored portion (not shown), preferably comprising a plurality of concave parabolic facets, for reflecting a portion of the intra-red light emitted by the transmitter back towards an infra-red receiver located adjacent the transmitter.

[0083] Means are provided for varying the intensity of light emitted by the transmitter 6 according to the amount of light reflected to ensure that the amount of infra-red light falling upon the receiver 26 of the earpiece 4 remains substantially constant regardless of the orientation of the person, a head and thus the distance and/or misalignment between the transmitter 6 and the earpiece receiver 26.

[0084] The infra-red receiver located adjacent the transmitter 6 may also or otherwise be used to adjust the intensity of light emitted by the transmitter according to ambient light levels.

[0085] A speaker 14 and a housing 28 depend on opposite sides of the earpiece, from respective halves 16, 18 of the clip 20, the housing 28 accommodating the re-chargeable power supply and electronic circuitry of the earpiece 4.

[0086] The earpiece 4 is fitted to a person's ear 12 as shown in FIGS. 7 and 8 by first separating the speaker 14 and housing 28 parts of the earpiece to open the clip 20 and then bringing the two parts 14, 28 back together, on opposite sides of the person's ear 12 such that the clip 20 becomes attached to the top of the ear 12, with the speaker 14 positioned within the ear, the housing 28 extending behind the ear and the telescopic rod 24 extending forwards from the ear.

[0087] A second embodiment of earpiece 4 is shown in FIG. 9, and comprises a parabolic concave mirror 30 for reflecting signals from the transmitter to a receiver located adjacent the speaker 14.

[0088] A third embodiment of earpiece 4 is shown in FIGS. 10 to 12 and, in an alternative configuration in FIG. 13, the earpiece comprising a tail portion 32 for hooking around the ear of the wearer, a portion 34 which, in use, extends forwards from the wearer's ear and a portion 36 which extends rearwards from the front of the device to support a microphone 38 over the external auditory canal of the wearer.

[0089] An elastomeric grip 40, fitted to the tail portion 32 of the earpiece is replaceable to allow the shape of the device to be readily modified to fit different sized and shaped ears and the device to be personalised to the wearer's taste by replacing the grip 40 with one of a different colour.

[0090] The front of the earpiece is provided with a window 42, behind which a pair of photosensitive devices are arranged to receive infra-red signals from above and below the earpiece respectively.

[0091] The tail portion 32 of the earpiece houses electronic circuitry and a rechargeable power supply.

[0092] The microphone 38 is rotatable about the axis of the rearwardly projecting portion 36, as illustrated in FIG. 13, to enable the earpiece to be configured for fitting either to the left or the right ear of the wearer.

[0093] Abutting parts of the portion 36 and a housing 44 of the microphone ensure that the microphone can only be rotated through 180 degrees between its left and right handed orientations.

[0094] A preferred transmitter unit 6 is shown in FIGS. 14 to 16 and comprises a main body 46, within which electronic circuitry and a re-chargeable power supply are housed, the body part 46 being provided at opposite ends with an infra-red emitter 48 and a lead 50 for connecting the transmitter to a mobile radiotelephone handset.

[0095] A clip 52 having an integral metallic fastening pin 53 is provided at the rear of the body part 46, for respectively clipping or pinning the transmitter unit to an outer garment of user, the clip 52 being detachable from the body part to be replaced by an alternative fastening device if required.

[0096] FIGS. 17 to 21 show a holder in the form of a case 54, having an internal tray 56 shaped to receive the earpiece and transmitter units of FIGS. 10 to 16, as shown in FIG. 19, for charging those devices either directly from an external power supply or via a rechargeable power source of the case.

[0097] The case 54 is provided with a socket 58 for connecting to said external power supply and two pairs of charging pins 60, 62 arranged to register with respective pairs of terminals 64, 68 formed in the bodies of the earpiece and transmitter units. A further pair of electrical contacts 70, 72 are arranged to be bridged by the fastening pin 53 of the transmitter unit 6, when that unit is fitted to the case, to complete a circuit for charging the earpiece 4.

[0098] The lid 74 of the case 54 is partially transparent, to provide a view of respective light emitting diodes (not shown) of the earpiece and transmitter units, which are illuminated whilst the devices are being charged. The same lights are preferably illuminated intermittently whilst the devices are operating (to provide an indication of whether the devices are charged), and are extinguished when their respective power supplies are exhausted.

[0099] An aperture 76 in the side of the case 54 provides a passageway through which the connecting lead 50 of the transmitter unit 6 may exit the case, to then be routed around a channel 78 formed in the sides of the case and secured in place by locating a connector at the end of the lead within a correspondingly shaped recess 80 formed in the base of the case.

[0100] The wireless, hands-free arrangements thus described provide a much safer and more convenient alternative to existing hand-free arrangements for use with mobile radio-telephone handsets. 

1) A hands-free kit for a mobile radio-telephone handset, the kit comprising an earpiece and an infra-red transmitter, the transmitter being arranged to relay audio signals from the handset to the earpiece, the earpiece comprising an infra-red receiver for receiving audio signals from the transmitter. 2) A hands-free kit as claimed in claim 1, wherein the transmitter communicates with the handset via a wired connection. 3) A hands-free kit as claimed in claim 1, wherein the transmitter communicates with the handset via a wireless connection. 4) A hands-free kit as claimed in any preceding claim, wherein the receiver is located at the distal end of a portion of the earpiece which, in use, projects forwards from the user's ear. 5) A hands-free kit as claimed in any preceding claim, wherein the receiver comprises a plurality of photosensitive devices arranged to receive infra-red signals from different respective directions including the direction of the transmitter. 6) A hands-free kit as claimed in any of claims 1 to 4, wherein means are provided on a forwards projecting portion of the earpiece, for reflecting audio signals from at least the direction of the transmitter towards the receiver. 7) A hands-free kit as claimed in any preceding claim, wherein the transmitter is arranged to be worn on the user's front, in line-of-sight of the earpiece receiver or of said eflecting means. 8) A hands-free kit as claimed in any preceding claim, comprising a microphone for connecting to the handset 9) A hands-free kit as claimed in claim 8, wherein the microphone comprises part of an integrated unit also comprising the transmitter. 10) if hands-free kit as claimed in claim 8 appended to claim 3, wherein the microphone and the transmitter each communicate with the handset via the same wireless connection. 11) A hands-free kit as claimed in any preceding claim, wherein the transmitter comprises a re-chargeable power supply. 12) A hands-free kit as claimed in any preceding claim, wherein the earpiece comprises a re-chargeable power supply. 13) A hands-free kit as claimed in claim 12 appended to claim 11, wherein the kit comprises a holder for the earpiece and the transmitter via which the re-chargeable power supplies of the two devices may be charged. 14) A hands-free kit as claimed in claim 13, wherein the holder is arranged to charge the earpiece and transmitter directly from an external supply. 15) A hands-free kit as claimed in claim 13, wherein the holder is arranged to charge the earpiece and transmitter directly via its own re-chargeable supply. 16) A hands-free kit as claimed in any of claims 13 to 15, wherein the holder is arranged prevent the earpiece from being charged independently of the transmitter. 17) A hands-free kit as claimed in any of claims 13 to 16, wherein the holder is arranged to prevent the transmitter from being charged independently of the earpiece. 18) A hands-free kit as claimed in any claim 15, wherein the holder is provided with means for visibly indicating its state of charge. 19) A hands-free kit as claimed in any of claims 13 to 18, wherein the holder is provided with means for visibly indicating the state of charge of the transmitter and/or of the earpiece. 20) A hands-free kit as claimed in claim 11 or claim 13, wherein the transmitter is provided with means for visibly indicating its state of charge. 21) A hands-free kit as claimed in claims 12 or claim 13, wherein the earpiece is provided with means for visibly indicating its state of charge. 22) A hands-free kit as claimed in claim 20 or claim 21 appended to claim 13, wherein the holder comprises a lidded case having a portion which is at least partially transparent and through which the charge indicating means of the transmitter and/or the earpiece may be viewed. 23) A hands-free kit as claimed in any of claims 18 to 22, wherein the or each said indicating means comprises a respective light. 24) A hands-free kit as claimed in claim 23, wherein said light is constantly illuminated, extinguished or illuminated intermittently to indicate different states of charge. 25) A hands-free kit as claimed in claim 11 or claim 12, wherein the earpiece emits an audible warning signal to indicate when the power supply of the transmitter and/or the earpiece is nearing exhaustion. 26) A hands-free kit as claimed in claim 25, wherein said audible signal comprises a periodic signal, which increases in frequency as the power supply of the earpiece and/or the transmitter is exhausted. 27) A hands-free kit as claimed in any preceding claim, wherein signals transmitted from the transmitter to the receiver are encrypted. 28) A hands-free kit as claimed in claim 27, wherein the transmitter and receiver are arranged to respectively encode and decode signals using a unique encryption algorithm. 29) A hands-free kit as claimed in claim 27, wherein the transmitter and receiver are arranged to respectively encode and decode signals using one of a plurality of encryption algorithms chosen on a random basis. 30) A hands-free kit as claimed in any of claims 27 to 29, wherein the transmitter and receiver are pre-programmed with an appropriate encryption key. 31) A hands-free kit as claimed in any of claims 27 to 29, wherein the encryption key is transmitted from the transmitter to the receiver 32) A hands-free kit as claimed in claim 31 wherein the encryption key is generated by the transmitter. 33) A hands-free kit as claimed in claim 32, wherein the encryption key is derived from the phone number or other identification code of the handset with which the hands-free kit is to be used. 34) A hands-free kit as claimed in claim 32, wherein the encryption key is chosen at random. 35) A hands-free kit as claimed in claim 34, wherein a new key, chosen at random, is transmitted to the receiver on a periodic basis. 36). A hands-free kit as claimed in any preceding claim, wherein the transmitter is arranged to transmit an identification signal to identify itself to the earpiece. 37) A hands-free kit as claimed in claim 36, wherein the identification signal is unique 38) A hands-free kit as claimed in claim 36, wherein the identification signal is chosen at random from one of a plurality of possible signals. 39) A hands-free kit as claimed in any of claims 36 to 38, wherein the transmitter and receiver are pre-programmed to operate using a particular identification signal. 40) A hands-free kit as claimed in claim 36 to 38, wherein the identification signal is communicated from the transmitter to the receiver 41) A hands-free kit as claimed in claim 40, wherein the identification signal is generated by the transmitter. 42) A hands-free kit as claimed in claim 41, wherein the identification signal is derived from the phone number or other identification code of the handset with which the hands-free kit is to be used. 43) A hands-free kit as claimed in claim 41, wherein the identification signal is chosen at random. 44) A hands-free kit as claimed in claim 43, wherein a new signal, chosen at random, is communicated to the earpiece on a periodic basis. 45) A hands-free kit as claimed in any of claims 36 to 44, wherein the earpiece is arranged to respond to an invalid identification signal by emitting an audible warning signal. 46) A hands-free kit as claimed in any of claims 36 to 45, wherein the transmitter is arranged to periodically transmit said identification signal within a stream of audio signals. 47) A hands-free kit as claimed in claim 46, wherein the earpiece is arranged to provide an audible alarm signal if a valid identification signal is not received over a predetermined period of time. 48) A hands-free kit as claimed in any preceding claim, wherein the earpiece is arranged to operate for periods in a standby mode, wherein one or more functions of the earpiece are disabled to conserve power. 49) A hands-free kit as claimed in claim 48, wherein the earpiece is arranged to enter the standby mode in the absence of a received signal. 50) A hands-free kit as claimed in claim 48 appended to any of claims 36 to 47, wherein the earpiece is arranged to enter the standby mode if a valid identification signal is not received. 51) A hands-free kit as claimed in any of claims 48 to 50, wherein the or each disabled function is restored in response to a received signal. 52) A hands-free kit as claimed in claims 51, wherein the or each disabled function is restored only if the received signal comprises a valid identification signal. 53) A hands-free kit as claimed in any of claims 48 to 52, wherein entry into the standby mode is immediate 54) A hands-free kit as claimed in any of claims 48 to 52, wherein entry into the standby mode is delayed. 55) A hands-free kit as claimed in any preceding claim, wherein the transmitter is arranged to operate for periods in a standby mode, wherein one or more functions of the transmitter are disabled to conserve power, in the absence of an audio signal from the handset. 56) A hands-free kit as claimed in any preceding claim, comprising a second infra-red receiver, located adjacent the transmitter, and means for varying the intensity of the infra-red light emitted by the transmitter according the amount of infra-red light received by the second receiver. 57) A hands-free kit as claimed in any preceding claim, arranged to provide a set-up mode, wherein the transmitter emits a light signal of substantially constant amplitude and the earpiece emits a periodic audible signal, whose periodicity varies in accordance with the amount of light received from the transmitter as the position of the transmitter is adjusted by a user. 58) A mobile radio-telephone arrangement comprising an earpiece and a mobile radio-telephone handset comprising an infra-red transmitter for relaying audio signals front the handset to the earpiece, the earpiece comprising an infra-red receiver for receiving audio signals from the transmitter. 59) A mobile radio-telephone arrangement comprising a mobile radio-telephone handset and a hands-free kit comprising an infra-red transmitter located at the breast of a user for relaying incoming audio signals from the handset to an earpiece worn by the user, the earpiece comprising an infra-red receiver arranged to receive audio signals from the transmitter. 60) An earpiece for attaching to an ear of a user and comprising an infrared receiver. 61) An earpiece as claimed in claim 60, wherein the receiver is arranged to receive signals from an infra-red transmitter positioned at the breast of a person wearing the earpiece. 62) An earpiece as claimed in claim 60 or claim 61, comprising a tail portion for hooking around the ear of the wearer, a portion which extends over and forwards from the user's ear and a portion which extends rearwards from the front of the device to position a microphone over the external auditory canal of the wearer. 63) An earpiece as claimed in claim 62, having an elastomeric grip fitted to the tail portion of the earpiece. 64) An earpiece as claimed in claim 63, wherein said elastomeric grip is replaceable. 65) An earpiece as claimed in any of claims 62 to 64, wherein the front of the earpiece is provided with a window, behind which a pair of photosensitive devices are arranged to receive infra-red signals from different respective directions. 66) An earpiece as claimed in any of claims 62 to 65, wherein the tail portion of the earpiece houses electronic circuitry and a rechargeable power supply. 67) An earpiece as claimed in any of claims 62 to 66, wherein said microphone is rotatable about the axis of said rearwardly projecting portion, to enable the earpiece to be configured for fitting to either the left or the right ear of the wearer. 68) An earpiece as claimed in claim 67, wherein abutting parts of the rearwardly projecting portion and a housing of the microphone ensure that the microphone can only be rotated through 180 degrees between its left and right handed orientations. 69) An infra-red transmitter arranged relay signals from a mobile radio-telephone handset to an earpiece worn by a user. 70) An infra-red transmitter as claimed in claim 69 arranged to be worn at the breast of the user. 71) An intra-red transmitter as claimed in claim 69 or claim 70 arranged to communicate with the handset via a wired connection. 72) An infra-red transmitter as claimed in claim 69 or claim 70 arranged to communicate with the handset via a wireless connection. 73) An audio apparatus comprising a headset, an infra-red transmitter for transmitting audio signals to the headset, an infra-red receiver located adjacent the transmitter and means for varying the intensity of the infrared light emitted by the transmitter according to the amount of infrared light received by the receiver. 